The invention presented herein relates to securing of boron filaments to each other and/or to a substrate and is particularly useful in the fabrication of boron-filament-containing tools for grinding, cutting, abrading or the like. Boron filaments as presently available are thin filaments or fibers of substantially elemental boron typically produced by depositing the boron of crystalline form on a fine tungsten core wire, the latter being a device for support during manufacture and while present in the filament does not enter into the cutting characteristics of the boron. The filaments or fibers are useful in cutting tool structures as a result of their super-high hardness and internal structure which allows them to fracture along lattice planes to always present a sharp edge at the filament tips.
Aside from the characteristic of wearing during cutting or abrading so as to continuously present a sharpened tip end, the boron filaments are sufficiently brittle to require adequate side support in order to prevent a too-rapid wear-away when cutting. The most desired arrangement places the adjacently disposed filaments in substantial side-by-side axial parallelism to present an "end on" array of closely spaced sharp filament ends at the working surface of a tool made therefrom. It has been found, however, that difficulties arise in attempting to provide a suitable matrix that is compatible with, that is, will attach itself to without degrading, the boron yet yields the requisite support suitable for tooling use. Prior to the herein disclosed development, making of boron-filament-containing cutting tools was directed primarily to the use of materials or combinations of them other than as herein presented and use of conventional powder metallurgy (i.e., other than as taught herein) or hot pressing in attempting to satisfactorily join or adhere boron filaments to themselves and to substrates in order to fabricate tool materials and shapes.
The disadvantages of such other methods and materials are several: Most cutting tools need high hardness only at the cutting surface, yet for some tool constructions where this surface is a narrow edge, use of older methods requires that considerable extra quantities of boron be chopped and placed in the tool body -- an extra expense and complication -- since known matrices were inadequate to otherwise produce the toughness and strength with preservation of filament integrity needed for some tool applications, e.g., where high compressive strength, or resistance to shear or bending forces are required. Also, prior materials and methods frequently resulted in excessive filament-to-matrix voids which contribute to low strength characteristics of the resultant filament/matrix or filament/matrix/substrate to defy the fabrication of thin wall shapes such as core drills. Further, with many matrices and materials high sintering temperatures and extended heating times deteriorate the boron filaments with resulting loss to their cutting and abrading properties. Still other difficulties have been encountered heretofore in getting the boron filament volume percentages high, when desirable, in the absence of a full liquid reaction type mixing of the matrix materials. It has also been found that boron-filament-containing tools and materials made under the prior powder metallurgy tend to have fairly low resistance to high impact loads which may be encountered in some machine or other tool applications so that there has been a need for a suitable matrix having the qualities of high strength and toughness which can encase and/or adhere the filaments into a satisfactory unitary structure in order to properly support and preserve the filaments and overcome the problems set forth above.